Method and apparatus for generating/transmitting a frame for wireless communication, and synchronization estimation method for wireless communication

ABSTRACT

Disclosed is a technique related to a method and apparatus for generating a preamble and a data frame for wireless communication, and to a synchronization estimation method using the preamble. According to the technique, a method for generating a frame for wireless communication is disclosed, wherein the method comprises: a step of generating a modified sequence using a first base sequence for synchronization estimation; and a step of allocating the first base sequence and the modified sequence to the frequency domain of a first timeslot to generate a preamble. The modified sequence includes a complex conjugated sequence of the first base sequence or a sequence having a code different from that of the first base sequence.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 16/685,507 filed onNov. 15, 2019, which is a continuation of U.S. application Ser. No.15/871,760 filed on Jan. 15, 2018 (now U.S. Pat. No. 10,484,221 issuedon Nov. 19, 2019), which is continuation of U.S. application Ser. No.13/392,468, filed on May 9, 2012 (now U.S. Pat. No. 10,277,443 issued onApr. 30, 2019), which is, in turn, a national stage of PCT applicationnumber PCT/KR2010/005591, filed on Aug. 23, 2010. Furthermore, thisapplication claims the foreign priority benefit of Korean applicationnumber 10-2009-0078935, filed on Aug. 25, 2009, and Korean applicationnumber 10-2010-0081409, filed on Aug. 23, 2010. The disclosures of theseprior applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and apparatus for generatingand transmitting a frame for wireless communication and asynchronization estimation method for wireless communication, and moreparticularly, to a method and apparatus for generating and transmittinga preamble and a data frame for wireless communication and asynchronization estimation method using a preamble.

BACKGROUND ART

A preamble may be used for time and frequency synchronization between atransmission side and a reception side that perform wirelesscommunication. The preamble may also be used for automatic gain control(AGC) and signal detection.

In particular, in a conventional Institute of Electrical and ElectronicsEngineers (IEEE) environment, a preamble may include two orthogonalfrequency division multiplexing (OFDM) symbols, each including a singlecyclic prefix (CP) and four repetition pattern (RP) sequences. That is,an RP sequence may be generated by assigning a complex sequence elementto a frequency domain with respect to four time intervals within apreamble interval. A CP may be generated using an RP sequence whereby asingle OFDM symbol may be generated. Another OFDM symbol may begenerated whereby the preamble may include two OFDM symbols.

DISCLOSURE OF INVENTION Technical Goals

An aspect of the present invention provides a method and apparatus forgenerating a frame for wireless communication that may generate apreamble capable of enhancing automatic gain control, signal detection,and time and frequency synchronization performances.

Another aspect of the present invention also provides a synchronizationestimation method for wireless communication using a preamble of astructure capable of enhancing automatic gain control, signal detection,and time and frequency synchronization performances.

Another aspect of the present invention also provides a method andapparatus for generating a frame for wireless communication that maygenerate a data frame capable of enhancing the data communicationefficiency.

Other features and advantages of the invention may be understood fromthe following description and be more apparent from embodiments of theinvention. Also, features and advantages of the invention may be easilyperformed by means disclosed in the claims and combinations thereof.

Technical Solutions

According to an aspect of the present invention, there is provided amethod of generating a frame for wireless communication, the methodincluding: generating a modified sequence using a first base sequencefor synchronization estimation; and generating a preamble by assigningthe first base sequence and the modified sequence to a frequency domainof a first time interval. The modified sequence may include a complexconjugate sequence of the first base sequence or a sequence having asign different from a sign of the first base sequence.

According to another aspect of the present invention, there is providedan apparatus for generating a frame for wireless communication, theapparatus including: a sequence generator to generate a modifiedsequence using a base sequence for synchronization estimation; and apreamble generator to generate a preamble by assigning the base sequenceand the modified sequence to a frequency domain of the same timeinterval. The modified sequence may include a complex conjugate sequenceof the base sequence or a sequence having a sign different from a signof the base sequence.

According to still another aspect of the present invention, there isprovided a synchronization estimation method for wireless communication,the method including: receiving a preamble from a station; andestimating synchronization with the station using the preamble. Thepreamble may be a preamble in which a base sequence for synchronizationestimation and a modified sequence of the base sequence are assigned toa frequency domain of the same time interval, and the modified sequencemay include a complex conjugate sequence of the base sequence or asequence having a sign different from a sign of the base sequence.

According to yet another aspect of the present invention, there isprovided a method of generating a frame for wireless communication, themethod including: generating modified data having a complex conjugateform of bit data, using the bit data; generating a data frame byassigning the bit data and the modified data to a frequency domain ofthe same time interval; and transmitting the data frame to a station.

According to a further another aspect of the present invention, there isprovided a method of transmitting a frame for wireless communication,the method including: generating modified data having a complexconjugate form of bit data, using the bit data mapping complexcoordinates; generating a data frame by assigning the bit data to a halfof the entire orthogonal frequency division multiplexing (OFDM)subcarriers according to predetermined frequency resources and byassigning the modified data to the remaining half of the OFDMsubcarriers in the same time interval; and transmitting the data frameto a station.

According to still another aspect of the present invention, there isprovided a method of receiving a data frame for wireless communication,the method including: receiving a data frame from a station; anddecoding the data frame. The data frame may be a data frame in which bitdata mapping complex coordinates and modified data having a complexconjugate type of the bit data may be assigned to a frequency domain ofthe same time interval.

Effect of the Invention

According to embodiments of the present invention, it is possible togenerate a preamble capable of enhancing automatic gain control, signaldetection, and time and frequency synchronization performances. Usingthe preamble, the complexity of a reception apparatus may decrease, andautomatic gain control, signal detection, and time and frequencysynchronization performances required for wireless communication may beenhanced.

Also, according to embodiments of the present invention, there may beprovided a data frame capable of enhancing the data communicationefficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a diagram to describe a preamble structure in anInstitute of Electrical and Electronics Engineers (IEEE) 802.11 wirelesscommunication system.

FIG. 2 and FIG. 3 illustrate diagrams to describe a method and apparatusfor generating a frame for wireless communication according to anembodiment of the present invention.

FIG. 4 illustrates a diagram to further describe a frequency domainassignment method described in FIG. 2 and FIG. 3.

FIG. 5 illustrates a diagram to describe a preamble structure accordingto an embodiment of the present invention.

FIG. 6 illustrates a diagram to describe a preamble structure accordingto another embodiment of the present invention.

FIG. 7 illustrates a diagram to describe a preamble structure accordingto still another embodiment of the present invention.

FIG. 8 is a flowchart illustrating a synchronization estimation methodfor wireless communication according to an embodiment of the presentinvention.

FIG. 9 is a flowchart illustrating a method of transmitting a frame forwireless communication according to another embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

For detailed description so that those skilled in the art may easilyimplement the technical spirit of the invention, exemplary embodimentsof the invention will be described with reference to the accompanyingdrawings. The above objectives, features, and advantages will be moreapparent from the following description associated with the accompanyingdrawings. When it is determined that detailed description related to theknown art may make the purpose of the invention unnecessarily ambiguousin describing the invention, the detailed description will be omittedhere.

FIG. 1 illustrates a diagram to describe a preamble structure in anInstitute of Electrical and Electronics Engineers (IEEE) 802.11 wirelesscommunication system.

As shown in FIG. 1, a preamble for synchronization estimation of IEEE802.11 may include two orthogonal frequency division multiplexing (OFDM)symbols 101 and 103. Each of the two OFDM symbols 101 and 103 mayinclude a total of five repetition pattern (RP) sequences, that is, fourRP sequences in a valid symbol interval and a single RP sequence in acyclic prefix (CP) interval. Four RP sequences in the valid symbolinterval may include an element of a base sequence for automatic gaincontrol, signal detection, and synchronization estimation every foursubcarriers. As shown in FIG. 1, the element, for example, E1 and E2, ofthe base sequence may be assigned to a subcarrier based on apredetermined RP. Here, inverse fast Fourier transform (IFFT) may beperformed with respect to the element of the base sequence. Here, thevalid symbol interval and the CP interval may indicate a time intervalof a time domain. The element of the base sequence may be assigned tothe frequency domain with respect to the valid symbol interval and theCP interval.

The single RP sequence in the CP interval may be generated byduplicating a last RP sequence of the valid symbol interval. A receptionend may perform automatic gain control, signal detection, and time andfrequency synchronization using the preamble of FIG. 1.

When using the preamble of FIG. 1, a reception side may need to use bothan auto-correlation method and a cross-correlation method together inorder to estimate synchronization. Accordingly, complexity may increasein a terminal of the reception side. Also, in the case of the preambleof FIG. 1, since a sequence having good correlation such as Zadofu-Chucomplex sequence is not used, a peak-to-average-power ratio (PAPR) mayincrease and there are some constraints on enhancing synchronizationestimation performance. In the case of the preamble of FIG. 1, since atime domain sequence element having a predetermined size for each sampleof an OFDM symbol is not used and an RP sequence by a base sequenceassigned to a frequency domain, indicating an inconsistent pattern in atime domain, is used, it may be difficult to further enhance automaticgain control and signal detection performances.

In the following, a preamble generation method capable of solving theaforementioned issues according to the present invention will bedescribed. An example of using wireless communication of an OFDM schemewill be described as an embodiment. Meanwhile, the term “station” usedin the following may be a concept that includes all of a source node, arelay node, and a destination node for cooperative communication andthus, may be a terminal or an access point (AP).

FIG. 2 and FIG. 3 illustrate diagrams to describe a method and apparatusfor generating a frame for wireless communication according to anembodiment of the present invention.

As shown in FIG. 2, a method of generating a frame for wirelesscommunication according to the present invention may be performedthrough operations S201 and S203. As shown in FIG. 3, a frame generationapparatus 300 for wireless communication according to the presentinvention may include a sequence generator 301 and a preamble generator303. Hereinafter, the frame generation method of the frame generationapparatus 300 will be described as an embodiment.

In operation S201, the frame generation apparatus 300 may generate amodified sequence using a first base sequence for synchronizationestimation. The modified sequence may include a complex conjugatesequence of the first base sequence or a sequence having a signdifferent from a sign of the first base sequence. That is, the framegeneration apparatus 300 may generate the complex conjugate sequence ofthe first base sequence or the sequence having the sign different fromthe sign of the first base sequence.

In operation S203, the frame generation apparatus 300 may generate apreamble by assigning the first base sequence and the modified sequenceto a frequency domain of a first time interval. That is, instead ofrepeatedly assigning a single base sequence element to a frequencydomain as described above with reference to FIG. 1, the frame generationmethod according to the present invention may generate a preamble byassigning the first base sequence and the modified sequence to afrequency domain. By assigning the first base sequence and the modifiedsequence to a frequency domain of the same time interval, a more robustperformance for a frequency offset may be obtained. A method ofassigning the first base sequence and the modified sequence to thefrequency domain will be further described with reference to FIG. 2.

Operations S201 and S203 may be performed by the sequence generator 301and the preamble generator 303 of FIG. 3. That is, the sequencegenerator 301 may generate the modified sequence using the first basesequence for synchronization estimation. The preamble generator 303 maygenerate the preamble by assigning the first base sequence and themodified sequence to the frequency domain of the first time interval.The preamble generated by the preamble generator 303 may be transmittedto a receiving side station through a transmitter 305.

FIG. 4 illustrates a diagram to further describe a frequency domainassignment method described in FIG. 2 and FIG. 3.

In FIG. 4, b_(u)(m) denotes a first base sequence. M_(u)(m) denotes amodified sequence and may be −b_(u)(m) or b*_(u)(m). Here, ‘*’ indicateschanging a sign of an imaginary portion value of a complex conjugate,that is, complex sequence element. ‘m’ indicates a sequence element as anatural number and ‘u’ denotes a sequence index. For example, b_(u)(0)may indicate a first element of the first base sequence.

As shown in FIG. 4, an element of the first base sequence and an elementof the modified sequence may be alternately or sequentially assigned tosubcarriers. More specifically, a block 401 indicates that the elementof the first base sequence and the element of the modified sequence aresequentially assigned to subcarriers. That is, in the block 401, thefirst base sequence and the modified sequence may be locally assigned. Ablock 403 indicates that the element of the first base sequence and theelement of the modified sequence are alternately assigned tosubcarriers. That is, in the block 403, the first base sequence and themodified sequence may be distributed and thereby be assigned.

An example in which all the frequency resources, that is, all thesubcarriers available in a frequency domain are used for assignment of afirst base sequence and a modified sequence is described as anembodiment. However, as described above with reference to FIG. 1, thefirst base sequence and the modified sequence may be repeatedly assignedto subcarriers every ‘n’ times and be nulled with respect to remainingsubcarriers. Here, ‘n’ indicates a natural number. That is, the elementof the first base sequence and the element of the modified sequence maybe assigned to subcarriers based on a predetermined RP.

The first base sequence may be a predetermined binary sequence or acomplex sequence. When the first base sequence is the complex sequence,the modified sequence may be a complex conjugate sequence of the firstbase sequence or a sequence having a sign difference from a sign of thefirst base sequence. When the first base sequence is the binarysequence, the modified sequence may be a sequence having a singdifferent from a sign of the first base sequence. Also, the modifiedsequence may be a sequence that is modified into another form, insteadof being the aforementioned sign converted or complex conjugatesequence. Also, the modified sequence may be a sequence identical to thefirst base sequence. Even in this case, similar to the above-describedmethod, the first base sequence and the modified sequence may beassigned to subcarriers.

A preamble structure according to embodiments of the present inventionwill be described with reference to FIG. 5 through FIG. 7. An NRP/NPsequence of FIG. 5 through FIG. 7 may correspond to a sequence describedabove with reference to FIG. 4.

FIG. 5 illustrates a diagram to describe a preamble structure accordingto an embodiment of the present invention.

As shown in FIG. 5, a preamble according to the present invention mayinclude a time division (TD) sequence 501, RP sequences 503, and anNRP/RP sequence 505. The RP sequence 503 may correspond to an RPsequence described above with reference to FIG. 1, and the NRP/RPsequence 505 may include a first base sequence and a modified sequencedescribed above with reference to FIG. 2 through FIG. 4.

The TD sequence 501 may be a binary sequence (or a complex sequencehaving good correlation) such as a pseudo-noise (PN)-spread binary phaseshift keying (BPSK) sequence (or a differentially encoded barker-spreadBPSK sequence or all other binary sequences having good correlation),and may be assigned to a TD sequence interval ahead of an RP sequenceinterval in which the RP sequences 503 are assigned. The TD sequence 501may be a sequence for automatic gain control or signal detection and beassigned ahead of a time interval in which the NRP/RP sequence 505 isassigned. That is, the frame generation apparatus 300 according to thepresent invention may generate a preamble by additionally assigning asecond base sequence, for example, the TD sequence 501, for automaticgain control or signal detection to a second time interval ahead of thefirst time interval. As described above with reference to FIG. 2, thefirst time interval may be a time interval in which the NRP/RP sequence505 is assigned.

In the second time interval, an element of the TD sequence 501 may havea constant amplitude. That is, the element of the TD sequence 501 mayhave a predetermined size for each sample of an OFDM symbol. Using asequence having a predetermined size for each sample of an OFDM symbol,automatic gain control and signal detection performances may be furtherenhanced. Time and frequency synchronization may be estimated throughthe TD sequence 501.

The NRP/RP sequence 505 may be a sequence in which the first basesequence and the modified sequence according to the present inventionare assigned. As described above, the NRP/RP sequence 505 may be robustin a frequency offset environment, and be used for precise frequency andtime synchronization estimation. Also, the NRP/RP sequence 505 may beused for rough time and frequency synchronization estimation togetherwith the RP sequences 503.

FIG. 6 illustrates a diagram to describe a preamble structure accordingto another embodiment of the present invention.

As shown in FIG. 6, a preamble according to the present invention mayinclude RP sequences 601 and an NRP/RP sequence 603. The preamble ofFIG. 6 may not include a TD sequence, which is different from thepreamble of FIG. 5.

FIG. 7 illustrates a diagram to describe a preamble structure accordingto still another embodiment of the present invention. An example inwhich a preamble includes two NRP/RP sequences 703 and 705 will bedescribed with reference to FIG. 7.

As shown in FIG. 7, a preamble according to the present invention mayinclude a TD sequence 701 and two NRP/RP sequences 703 and 705. Thepreamble of FIG. 7 may not include an RP sequence and may include twoNRP/RP sequences, which is different from the preamble of FIG. 5. Thatis, the frame generation apparatus 300 according to the presentinvention may generate a preamble by additionally assigning a first basesequence and a modified sequence to a time domain of a third timeinterval. In this instance, the frame generation apparatus 300 maygenerate a preamble that includes at least one NRP/RP sequence in a timeinterval after the third time interval.

Here, a sign of the first NRP/RP sequence 703 with respect to the firsttime interval and a sign of the second NRP/RP sequence 705 may beidentical to each other or may be different from each other. That is, apair of the same signs or a pair of different signs may be assigned toelements of the first NRP/RP sequence 703 and elements of the secondNRP/RP sequence 705. That is, signs may be assigned in a form of (+, +),(+, −), and (−, +)).

More specifically, when a sign pair pattern with respect to elements ofthe first NRP/RP sequence 703 and the second NRP/RP sequence 705 is (+,−), signs may be assigned to a preamble by maintaining signs of theelements of the first NRP/RP sequence 703 and by changing signs of theelements of the second NRP/RP sequence 705. When at least three NRP/RPsequences are assigned to a preamble, signs may be assigned to thepreamble by only changing signs of elements of a last NRP/RP sequence.

Even though a CP is not included in a preamble described above withreference to FIG. 5 through FIG. 7, a CP with respect to a TD sequence,an RP sequence, and an NRP/RP sequence may be included.

FIG. 8 is a flowchart illustrating a synchronization estimation methodfor wireless communication according to an embodiment of the presentinvention.

As shown in FIG. 8, the synchronization estimation method according tothe present invention may be initiated from operation S801. In operationS801, a reception station may receive a preamble from a transmissionstation. In operation S803, the reception station may estimatesynchronization with the transmission station using the preamble. Here,the preamble may be a preamble described above with reference to FIG. 2through FIG. 7. That is, the preamble received by the reception stationmay be a preamble in which a base sequence for synchronizationestimation and a modified sequence of the base sequence are assigned toa frequency domain of the same time interval. The modified sequence mayinclude a complex conjugate sequence of the base sequence or a sequencehaving a sign different from a sign of the base sequence.

As described above, the preamble described above with reference to FIG.2 through FIG. 7 may be robust against a frequency offset, and thesynchronization estimation performance of the reception stationreceiving a preamble according to the present invention may be enhanced.Due to the enhancement of synchronization estimation performance, thecomplexity of the reception station may decrease. Each operationconstituting the synchronization estimation method according to thepresent invention may be easily understood from view of an apparatus,and may be understood as a constituent element included in the receptionstation.

The above-described frame generation method may be applied even whengenerating a data frame. That is, instead of generating a sequence forsynchronization estimation, a data frame in which bit data is assignedto a frequency domain may be generated. Hereinafter, FIG. 9 will bedescribed.

FIG. 9 is a flowchart illustrating a method of transmitting a frame forwireless communication according to another embodiment of the presentinvention. As shown in FIG. 9, the frame transmission method accordingto the present invention may be initiated from operation S901.

In operation S901, a station performing wireless communication maygenerate modified data having a complex conjugate form of bit data,using the bit data. In operation S903, the station may generate a dataframe by assigning the bit data and the modified data to a frequencydomain of the same time interval. In operation S905, the station maytransmit, to a reception station, the data frame that is generated inoperation S903.

Here, as described above with reference to FIG. 4, the station maygenerate a data frame by alternately or sequentially assigning bit dataand modified data to subcarriers. When the bit data and the modifieddata is sequentially assigned to subcarriers, the bit data may beassigned to a half of the entire subcarriers according to predeterminedfrequency resources, and the modified data may be assigned to theremaining half thereof.

For example, when a total number of available subcarriers is eight, bitdata may be assigned to first to fourth subcarriers, and modified datamay be assigned to fifth to eight subcarriers. That is, bit data may beassigned to a half of OFDM subcarriers according to predeterminedfrequency resources, and modified data may be assigned to the remaininghalf of OFDM subcarriers whereby a data frame may be generated. Here,the bit data may be data that include a plurality of symbols mappingcomplex coordinates. That is, the bit data may be data in theaforementioned complex sequence form. The modified data may be in acomplex conjugate form of the bit data.

The modified data and the bit data may be identical to each other. Evenin this case, the bit data and the modified data may be assigned to thefrequency domain using the above-described method.

The frame transmission method of FIG. 9 may also be readily understoodfrom view of an apparatus. That is, each operation constituting theframe transmission method of FIG. 9 may be easily understood from viewof an apparatus, and may be understood as a constituent element includedin the station. The reception station receiving the above data frame maydecode the data frame. That is, the reception station may receive a dataframe from a transmission station, and may decode data using thereceived data frame. The data frame reception method may also beunderstood as a constituent element included in the station.

The above-described frame generation method, frame reception method, andsynchronization estimation method for wireless communication accordingto the present invention may be recorded as a computer program. A codeand a code segment constituting the program may be readily inferred by acomputer programmer in the field. Also, the program may be stored incomputer-readable recording media (information storage media) and may beread and executed by a computer, thereby implementing the method of thepresent invention. The recording media may include any types ofcomputer-readable recording media, for example, tangible media such asCD and DVD and intangible media such as subcarriers.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

1. A communication method, the method comprising: identifying a firstsequence; identifying a second sequence derived from the first sequence;and allocating the first sequence and the second sequence into asub-carrier, wherein a ratio of the first sequence and the secondsequence allocated in the sub-carrier is 1:1, wherein the first sequenceis allocated into an upper portion of the sub-carrier and the secondsequence is allocated into a lower portion of the sub-carrier.
 2. Thecommunication method of claim 1, wherein the second sequence isdetermined by applying −1 into the first sequence.
 3. The communicationmethod of claim 1, wherein the second sequence is determined by applyingcomplex conjugation into the first sequence.
 4. The communication methodof claim 1, wherein the first sequence is allocated sequentially intothe upper portion of the sub-carrier, and the second sequence isallocated sequentially into the lower portion of the sub-carrier.
 5. Thecommunication method of claim 1, wherein a first index of the firstsequence in the upper portion of the sub-carrier corresponds to a firstindex of the second sequence in the lower portion of the sub-carrier. 6.A communication method, the method comprising: identifying a firstsequence; identifying a second sequence derived from the first sequence;and allocating the first sequence and the second sequence into asub-carrier, wherein a ratio of the first sequence and the secondsequence allocated in the sub-carrier is 1:1, wherein the first sequenceis allocated into a lower portion of the sub-carrier and the secondsequence is allocated into an upper portion of the sub-carrier.
 7. Thecommunication method of claim 6, wherein the second sequence isdetermined by applying −1 into the first sequence.
 8. The communicationmethod of claim 6, wherein the second sequence is determined by applyingcomplex conjugation into the first sequence.
 9. The communication methodof claim 6, wherein the first sequence is allocated sequentially intothe upper portion of the sub-carrier, and the second sequence isallocated sequentially into the lower portion of the sub-carrier. 10.The communication method of claim 6, wherein a first index of the firstsequence in the lower portion of the sub-carrier corresponds to a firstindex of the second sequence in the upper portion of the sub-carrier.